1.) Field of the Invention
The present invention relates to a large-capacity information processing system in which a library unit and a storage unit are disposed in hierarchical relation.
2.) Description of the Related Art
In general, a large-capacity information processing system (information managing system) has principally employed a library unit functioning as a large-capacity external storage unit. This library unit, accommodating a large number of recording mediums such as a magnetic tapes or optical disks, has a function to gain access automatically to data in each recording medium.
However, the readout processing or write processing on information between this library unit and a data processing apparatus (for example, host computer) requires extremely much time, which has forced the library unit to use as a backup unit.
Meanwhile, although a hard disk unit (storage unit) having a hard disk (magnetic disk) is capable of gaining high-speed access, it requires an overwhelming higher cost in comparison with a magnetic tape, an optical disk or the like, so difficulty is experienced in realizing a large-capacity information processing system employing only a hard disk.
For this reason, an information processing system (which will hereinafter be referred to as a “hierarchical storage system”) has been employed, which realizes low cost and high-speed access simultaneously in such a manner as to arrange high-speed access-gainable hard disk units (storage units) and library units hierarchically (for example, see Japanese Patent Laid-Open No. HEI 5-88975).
However, since the hierarchical storage system disclosed in Japanese Patent Laid-Open No. HEI 5-88975 is designed to efficiently manage data between a library unit and a hard disk unit through the use of management on a host computer which issues a request on access to data, the host computer serving as a user is required to pay attention to each of the library unit and the hard disk unit.
In addition, management software, which is for managing the hierarchical storage (library unit and hard disk unit), is provided on the host computer, and this bears heavily not only upon the resources of the computer but also the user's network resources because there is a need to make, through the use of a LAN (Local Area Network) or the like, a connection between the host computer and the library unit and a connection between the host computer and the hard disk unit.
Therefore, there has been proposed a technique in which, instead of on a host computer, management software for the management of a hierarchical storage is provided on a hierarchical storage to achieve the management through the hierarchical storage itself without using the resources of a host computer serving as a user (for example, Japanese Patent Laid-Open No. 2000-235457).
Meanwhile, in a case in which, after the issue of a host I/O (Input/Output; input/output request), the waiting time for a response to this I/O exceeds a predetermined period of time, a host computer has so far been made to detect the time-out (error) for canceling the processing on this I/O request, which avoids a wasteful long waiting time for the host I/O, thus achieving efficient processing.
Although it is desirable that a host computer detects the time-out even in the technique disclosed in Japanese Patent Laid-Open No. 2000-235457, if a hard disk unit does not retain data which is an object of an access request (I/O request) issued from the host computer (data which is an object of processing in the host computer), in the case of the technique disclosed in Japanese Patent Laid-Open No. 2000-235457, there is a need to read out this processing data from a library unit. Thus, in the case of the issue of access to the library unit, an extremely longer waiting time occurs in the host computer in comparison with the case in which the hard disk unit retains the processing data.
For this reason, even if the hierarchical storage system disclosed in Japanese Patent Laid-Open No. 2000-235457 employs a facility designed so that a host computer detects the time-out, in a case in which the processing data is read out from the library unit, a long waiting time occurs in the host computer even though it is in a normal operation according to an access request from the host computer, which can cause the host computer to detect the time-out (error).